The present invention relates to concrete paving.
The technology for providing concrete paving that has surface features has become an important field of endeavor with the advent of Americans with Disabilities Act (ADA) current guidelines requirement for detectable warnings on walking surfaces. These detectable warnings must be a grid of raised truncated domes with a diameter of 23 mm (0.9 in) at the base and 10 mm (0.4 in) at the top, a height of 5 mm (0.2 in) and a center-to-center spacing between nearest neighbors of 60 mm (2.35 in).
A number of different technologies have evolved to create the detectable warnings. First there is a polymer molded product that is about 5 mm (0.1875 in) thick and is provided in the form of tiles having flanges that extend downwardly by 3.5 cm (1.375 in). To install this product, the flanges are pressed into wet concrete. This material is light, and therefore easy to bring to the worksite. It may form a strong bond with the concrete that it is applied onto. Moreover, the fact that it is applied onto wet concrete is a great advantage, as it can be applied at the same time as the concrete is poured, unlike some other methods that are described below. The general term for this type of product is a “wet set” plastic tile.
A number of other surface feature-bearing elements exist, including precast concrete blocks, on the order of 5 cm (2 in) thick, brick pavers, glue down plastic elements, glue down rubber mat and hot applied mat. Unfortunately, for each one of these options, the installer must first pour a concrete substrate, wait 28 days for the concrete to thoroughly set, and then return to apply the surface feature bearing elements. This has been heretofore necessary for any product that had a thickness of more than a few millimeters, as the surface bearing element would otherwise protrude upwardly above the surrounding surface. Precast concrete blocks have had the particular problem that they are so heavy that if set into wet concrete such a block would press down so heavily as to push the wet concrete up around the sides of the concrete block. Any glue down product must be adhered to a finished substrate in order to gain a strong adhesion. Moreover, brick pavers must be laid on an even finished surface. Because they are supported by a substrate that is already solid at the time of installation, all of these products tend to have substantially planar bottom surfaces.
In a separate sequence of developments, prestressed concrete has been available for many years, with improvements gradually being made to the production process and the resultant product. A relatively recent advancement is described in U.S. Patent Application Publication 2002/0059768 (“the application”), which is incorporated by reference as if fully set forth herein. The application describes a method for producing a thin, lightweight prestressed concrete panel by balancing the tendons about a center plane of the panel. There appears to be no suggestion in the application that the panels thereby produced could be beneficially used as paving tiles.
Moreover, at first assessment, it would seem to many of those familiar with the technology of concrete installations that the use of this type of panel for paving would be limited to applications in which a substrate of cured concrete first must be provided. This appears to be how the previously available concrete blocks and all of the adhered paving elements have been installed. Moreover, the added expense of using prestressed concrete for applications in which there is not a structural requirement to do so, would not appear practical.